Reaction end-point recorder for use with a rotary analytical photometer

ABSTRACT

An analog data recording system has been provided for recording data values from a rotary analytical photometer. The system comprises means for scanning the range of data values, comparing the data values with the instantaneous value of a logarithmic scan voltage and energizing individual marking means that are synchronized with the scan when the voltage value of the scan equals the individual data voltage value.

United States Patent 1 1 7 Johnson et al.

REACTION END-POINT RECORDER FOR USE WITH A ROTARY ANALYTICAL PHOTOMETERInventors: Wayne F. Johnson, Loudon; William R. Miller, Oak Ridge, bothof Tenn.

The United States of America as represented by the United States AtomicEnergy Commission,-

, Washington, DC

Filed: Nov. 9, 1971 Appl. No.: 196,900

Assignee:

US. Cl. 346/74 E, 346/35 Int. Cl. G011 23/18, GOld 5/243 Field ofSearch...... 340/1741 A, 174.1 G;

346/74 ES, 74 M, 74 E, 74 SB, 74 so, 33 R,

. 35; 324 77 D, 77 E I 1 1 June 19, 1973 References Cited UNITED STATESPATENTS 3,611,411 10/1971 Moshier 346/74 E 3,631,509 12/1971 Marshall346/74 E Primary Examiner-Vincel1t P. Canney Attorney-Roland A. Anderson[57] ABSTRACT An analog data recording system has been provided forrecording data values from a rotary analytical photometer. The systemcomprises means for scanning the range of data values, comparing thedata values with the instantaneous value of a logarithmic scan voltageand energizing individual marking means that are synchronized with thescan when the voltage value of the scan equals the individual datavoltage value. v

10 Claims, 1 Drawing Figure PATENIEB aux pggauuoauz REACTION END-POINTRECORDER FOR USE WITH A ROTARY ANALYTICAL PHOTOMETER BACKGROUND OF THEINVENTION The present invention was made during the course of, or under,a contract with the U. S. Atomic Energy Commission. v

This invention relates generally to analog recording apparatus for usewith data acquisition systems and more specifically to an analogrecording system for use with an analytical photometer wherein the datavalues are in the form of a continuously repeating train of pulses.

In the past, various means have been provided for recording data valuesfrom photometric analyzers of the high speed, parallel type, such asthat disclosed in U. S. Pat. No. 3,555,284, issued Jan. 12, 1971, andhaving a common'assignee with the present application. In these machinesa plurality of discrete samples in individual glass or plastic cuvettesare moved past stations'where additions, reactions, or measurementsoccur. Typically, the cuvettes are formed ina rotating assembly having aplurality of stations around the circumference designed to holdreagents, catalysts, standards, or samples under test. As the assemblyis'accelerated, all samples and reagents are mixed simultaneously in thecuvettes. The light transmission of the mixtures is then measured bypassing light through the cuvettes as they pass a measuring stationwhere a light detector, such as a photomultiplier tube, generates apulse for each cuvette as it passes the station. These pulses are in theform of a continuously repeating train of pulses, each pulse amplituderepresenting the light transmittance of each cuvette sample or standardas the case may be.

It has been the practice to use a digital computer with an appropriateinterfacing system to allow direct readin of sample data. The computeris programmed to perform various necessary computations for desired datareduction and readout.

More recently, attention has turned to smaller versions of the abovemachines for use in laboratories where access to a digital computer isnot practical or feasible. Accordingly, the present invention is theresult of an effort to provide an inexpensive apparatus for recordinganalytical photometer data values, particularly apparatus to record thevalues of a run on a single card. i

SUMMARY OF THE INVENTION In view of the above-state need it is an objectof this invention to provide a simple and inexpensive analog datarecording apparatus for use in recording the individual amplitude of arepeating train of data pulses.

Another object of this invention is to provide an analog recordingapparatus having a plurality of recording channels corresponding to thenumber of data pulses in a repeating train of pulses which records theamplitude of each of these pulses in respective channels.

Yet another object of this invention is to provide an analog recordingapparatus as in the above objects for use with a high-speed photometricanalyzer which records data in the form of sample concentration by alogarithmic conversion from measured sample transmittance values.

Briefly, the invention comprises a means for receivin g a repeatingtrain of data pulses of varying amplitude and comparing the amplitude ofeach data pulse with a scanning reference voltage to generate an outputwhen the amplitude of a data pulse equals or exceeds that of thereference voltage, a means for generating reference pulses synchronizedwith the data pulses and repeatedly sequentially generating enablingpulses to a plurality of separate gating inputs corresponding to thenumber of data pulses of the repeating train of pulses, and a pluralityof gating means equal to the plurality of outputs of said referencepulse generating means, each of the gating means having a trigger inputconnected to the output of the comparator means and an enabling inputconnected to respective outputs of reference pulse generating means sothat a pulse is provided at the output of each gate the first time apulse is applied to the trigger input, indicating that a data signal hasexceeded the reference voltage. A recorder is provided that includes alinearly movable carriage having a plurality of electrically operatedmarkers connected to respective outputs of the gating means so that arecord card is marked in the appropriate channel at a distance from areference position to indicate its amplitude as the carriage moves overthe record card, and a drive means which drives the carriage and avariable voltage divider to provide the scanning reference voltage.

Other objects and many'of the attendant advantages of the presentinvention will be obvious from the following detailed description of theinvention taken'in conjunction with the drawing, wherein the single FIG- URE is a schematic diagram of an analog recording apparatusaccording to the present invention.

DETAILED DESCRIPTION Referring now to the drawing, a portion of thephotometric analyzer, as described in the above-referenced U. S. Pat.No. 3,555,284, is shown schematically and generally indicated byreference number 5. The analyzer rotor 7 is power driven by aconventional drive means (not shown). Disposed within the rotor 7 are aplurality of sample-containing cuvette chambers, one below each of thelight path defining holes 9. The rotor 7 has attached thereto, forsynchronous rotation therewith, a synchronization disc 11. The disc 11has a' plurality of slotted openings 13 radially positioned adjacent theperiphery of the disc 11. Each slot 13 is in a particular alignment witha corresponding one of the plurality of-cuvette chambers so as toprovide a synchronizing pulse, here termed the cuvette pulse, during thepassing of a cuvette past a sensor position. The disc 11 is alsoprovided with one slot 15 which is aligned with the rotor 11 at a radialposition inward of the slots 13 so as to provide an additional pulse,here termed the rotor pulse, as the rotor spins. This slot 15 is alignedso that the rotor pulse occurs slightly before the illumination ofcuvette in position No. l on the rotor 7. I

In order to provide the cuvette pulses and the rotor pulse, a pair ofphotodetectors 23 and 25 are mounted so as to view light from sources 19and 21, respectively, directed through the slots 13 and 15. Each time aslot 13 passes the sensor or measuring position a cuvette pulse isgenerated and once each revolution a rotor pulse is generated when slot15 passes the measuring position to indicate the first of the train ofdata pulses from the analyzer.

A third photodetector 27 is disposed above the rotor 5 and aligned tosense light transmitted through the cuvettes during rotation from alight source 29 and a mirror 31 disposed below the rotor assembly andoriented to reflect the light beam upward, substantially normal to theplane of rotation of the rotor. The photodetector 27 may be aphotomultiplier tube or photocell disposed directly above the cuvettecircle at the sensor or measuring position to receive light transmittedthrough axially aligned openings 9. Each time a cuvette opening 9 passesthe measuring position, a data pulse is generated whose amplitude isindicative of the light transmittance of the sample relative to astandard or blank cuvette.

The output of photomultiplier 27 is connected to the non-inverting inputof an operational amplifier 31 whose inverting input is connected to abias network 75. The output of amplifier 31 is connected through asumming resistor 33' to the input of a comparator 35. The input ofcomparator 35 is also connected to the motor driven wiper of alogarithmic potentiometer 37 by means of a summing resistor 39. Thelogarithmic potentiometer 37 provides a logarithmically varyingreference voltage connected to a positive voltage source by means of avariable calibrating resistor 38 whose function will be describedhereinbelow.

The two inputs to comparator 35 are connected to its inverting input andits output is connected to a zener diode 72. The output of comparator 35is held at zero volts by diode 72 when the sum of the inputs tocomparator 35 is positive, andwhen this sum is negative, the output ofcomparator 35 is at the proper signal level for the circuitry whichfollows. Thus so long as the sum of the input voltage to comparator 35is positive (reference voltage greater than data pulses) the output isat zero volts. When the input signal goes negative, as when one of thedata pulses exceeds the reference voltage, a fixed amplitude positivepulse is generated for the duration of the data pulse.

The output of the comparator 35 is connected to the trigger inputs of aplurality of J-K flip-flops 41, in this case 16, of which only the firstand last (16th) are shown in order to simplify the drawing.

Referring again to the analyzer 5, the cuvette pulses detected byphotodetector 23, which are generated synchronously with the particulardata signal pulses,

are applied to the input of an amplifier 43 which drives a pulse shaper45'. The pulse shaper 45 provides a fixed duration pulse for each inputpulse which activates a binary counter 47 to increase the count by onefor each cuvette pulse. Counter 47 is a 4-bit counter, thus having a 16count capacity. Each of the 4 counter bits is connected to a sixteenchannel decoder 49. The decoder 49 is of conventional design wherein oneof sixteen outputs is activated in accordance with the binary code countregistered by the counter 47. The sixteen outputs of the decoder 49 areconnected, respectively, to the enabling inputs of flip-flops 41.

Since the. pulses to be recorded are repeating, it is necessary to resetthe circuit each time the last rotor cuvette position passes themeasuring station. This is accomplished by the rotor pulse at the outputof photodetector 25 which is connected to an amplifier 42 which drives apulse shaper 46. The output of the pulse shaper 46 is connected to thereset input of the counter 47 which resets the counter 47 to its initialstate of an output of bit 1 at the beginning of each revolution of therotor ,7.-

' The set outputs of flip-flops 41 are connected to individual one-shotsolenoid drivers 53. Each of the drivers 53 includes a pair oftransistors with a positive feedback R-C network to stretch theactivating pulse duration to produce the desired pulse to drive thesolenoid coils 55. The outputs of drivers 53 are connected,respectively, to the drive coils of sixteen solenoid actuated pens 55.The pens 55 are mounted in a carriage 57 of a recorder 56 which isadapted for travel over a record card 59 so that when the ssolenoid of apen is activated it will print a mark in the corresponding one ofsixteen channels indicated on the card 59.

The carriage 57 is driven linearly along the card by means of drivescrews 61 and 63 adapted for threaded engagement of the carriage atopposite ends thereof. Drive screw 61 is connected to the shaft of areversible motor 65 which drives both screws by means of a belt drive 67connected between screws 61 and 63. The movement of the carriage iscontrolled by limit switches 69 and 71. Switch 69 is a normally closedswitch (i.e., closed when not being activated by the carriage) whileswitch 71 is a normally open switch, as indicated schematically in thedrawing.

Limit switches 69 and 71 are connected in series with a relay K2 and theseries circuit is connected across the 115 volt AC supply. Relay K2 hastwo sets of normally open contacts, K2A and K2C, and one set of normallyclosed contacts, K2B. Contacts K2A are connected in parallel with limitswitch 71. A second relay K1 is connected in series between the supplyand neutral with the normally closed contacts K28 and a momentary pushstart switch 73. Relay K1 has two sets of normally open contacts, KIAand KlB, and one set of normally closed contacts, KlC. Contacts KIA areconnected in parallel with start switch 73 so that, when switch'73 ispushed to start a recording scan, relay K1 is activated and locked in bythe closing of contacts KIA. Contacts KIB are connected between thevoltage supply and the up input of motor 65, so that the closing ofcontacts KIB causes the motor to turn counterclockwise, driving thecarriage up.'Contacts K2C of relay K2 are connected between the voltagesupply and the down input of motor so that the closing of contacts K2Ccauses the motor to rotate clockwise driving the carriage down once ithas reached limit switch 71. When the carriage 57 reaches limit switch71, it closes, thereby energizing relay K2 (switch contacts69 beingnormally closed) and in turn opening contacts K2B causing relay K1 todrop out. Contacts K2C are closed and contacts KlB are opened, therebycausing the motor 65-to reverse and drive the carriage 57 down to thestart position. Since contacts K2 A are closed, relay K2 remains lockedin until the carriage reaches the lower limit switch 69. When switch 69opens, relay K2 drops out and a print cycle is completed.

It will be noted that contacts KlC are connected between the reset (R)input of flip-flops 41 and ground so that at any time that K1 is notenergized contacts KlC are closed applying ground potential to the resetinputs, thereby resetting the flip-flops tostart another scan.

During operation, an external device such as the photometric analyzer 5is repeatedly presenting the following signals: a train of sixteennegative going data pulses normally within the range of 0-10 V to theinput of non-inverting amplifier 31; a train of sixteen sequenceidentifying (reference) pulses, as in this case the euvette pulses insynchronism with the data pulses to the input of amplifier 43; and asingle pulse for identification (rotor pulse) that occurs just prior tothe first of the train of sixteen data pulses and applied to the setinput of amplifier 42.

Assuming that the system has been calibrated by setting thepotentiometer 38 at a value corresponding to the light transmittance ofa known standard, such as water, the rotor is placed in rotation and thestart switch 73 depressed momentarily to start the recorder 56scanningsequence as described above. When motor 65 starts, thecarriagev57 begins to move up and the scanning arm of the logarithmicpotentiometer 37 begins to move toward a decreasing positive voltage.

Since the motor 65 speed inoves relatively slow compared to the speed ofthe rotor 7 of analyzer 5, the voltage of potentiometer 37 will not havechanged significantly and no recording will be made prior to theapplication of the first rotor pulse from detector 25. This pulse resets the counter 47 so that the first cuvette pulse is counted in theproper sequence and applies the proper code to decoder 49. As the scancontinues, eventually the positive voltage from potentiometer 37 moveslinearly over the record card 59 with respect to r the logarithmicallyvarying reference voltage from the will reach a value which compares tothe amplitude of I a negative data pulse from amplifier 31 and willcause the input of comparator 35 to go positive (the negative data pulsevoltage exceeding the reference voltage from potentiometer 37). Thisprovides a positive going pulse at the outputof comparator amplifier 35which is applied tothe trigger inputs of all sixteen flip-flops 41.However, at the same instant the particular cuvette number registered incounter 47 activates decoder 49 to apply an enabling pulse only to theparticular corresponding number flip-flop 41, causing it to set andthereby apply a pulse to the corresponding numbered solenoid driver'53which, in turn, activates th'ecorresponding numbered pen 55 to mark thecard 59 in the appropriate channel corresponding of the cuvette number.For example, assume that the highest transmittance value sample islocated in cuvette position No. l, the counter 47 will have registeredone count and thus the decoder 49 will have an output on line 1. Thedata pulse will exceed the reference voltage and thus the 'output ofcomparator 35 will go positive for the duration of the data pulsei Thiscauses the first one of flipflops 41 to go set, thereby activating theNo. l pen through the corresponding one-shot driver 53. Once a flip-flop41 is set, it remains set until reset by the closing of contacts KlC.The one-shot drivers 53 are then only activated one time, even thoughthe inputs from flip-flops 41 remain high throughout the remainder ofthe scan.

As pointed out above, the rotor pulse from detector v25 which is set tooccurjust prior to the reading of the No. l cuvette is used to reset thecounter 47 to its initial state of an output of bit "1 to begin thesynchronous count with the rotation of the rotor 7.

Accordingly, it will be seen that the scan continues until all thesamples are read and carriage 57 of the recorder 56 reaches limit switch71 and returns to the initial position, against limit switch 69. Theflip-flops'41 are held inactive during the return of the carriage 57 bymeans of the ground applied through contacts KlC during the returntravel of carriage 57 in order to prevent an erroneous activation of oneof the pens 55.

It should be noted here that a logarithmically varying potentiometer 37has been employed. It will be understood that byemploying thispotentiometer the transmittance values measured by the photomultiplier27 output which varies linearly'with transmittance values of thesamplesthe samples converted to an absorbance or concentration measurementsince the carriage 57 scanning potentiometer 37.-Thus, considering theinitial calibration of the system there is provided a direct recordingof concentration of the samples which is determined by the distance arecord print is made on the card from the lower or reference position ofthe carriage 57.

It will be understood that it would be obvious to those skilled in theart that other recordings could be made depending on the application.For example, the refer ence potentiometer 37 could be made to varylinearly.

and thereby provide a linear record of the data values without anytransformation of the data. This feature contributes an inherentversatility in that changeover to other scales can be provided withlittle additional cost or complication.

Although the device has been illustrated for use with a sixteen stationphotometric analyzer, it is neither limited to this application alonenor to only sixteen channels or a train of sixteen repeating pulses. Thedevice could be used for any number of pulses as long as the counter 47and decoder 49 are arranged-to provide a corresponding number of recordchannels.

What is claimed is: I

1. An analog data recording apparatus for recording a plurality of datavsignals which are in the form of a continuously repeating train ofelectrical pulses of varying amplitude, comprising:

a comparator means for receiving said repeating train of pulses at aninput thereof and comparing the amplitude of each of said pulses with ascanning reference voltage and providing a pulse at an output thereofeach time the amplitude of one of said data signals exceeds saidreference voltage;

amechanically driven variable voltage source having an output connectedto said comparator means for providing said scanning reference voltage;

means for generating reference pulses and repeat edly, sequentiallyapply each reference pulse to'a plurality of separate outputscorresponding to the number of data signals of said repeating train ofpulses;

'a plurality of gating means equal to said plurality of outputs of saidreference pulse generating means, each of said gating'means havingatrigger input commonly connected to the output of said comparator meansand an enabling input connected to respective outputs of said referencepulse generating means for providing an output pulse at an outputthereof the first time a pulse is applied to said input thereof fromsaid reference pulse generating means in coincident with a pulse fromsaid comparator means;

recorder means including a linearly movable carriage having a pluralityof electrically operated markers, each of said markers having an inputconnected to respective outputs of said plurality of gating means;

a record medium disposed under said carriage; and

a drive means mechanically coupled to said carriage and said variablevoltage source for synchronously moving said carriage over said recordmedium and adjusting the voltage output of said variable voltage sourcein a scanning mode, whereby each of said markers is activated to marksaid record medium at a distance from a reference position on saidrecord medium when the corresponding data signal exceeds said referencevoltage level of said variable voltage source.

2. An analog data recording apparatus as set forth in claim 1 whereinsaid reference pulse generating means includes a binary counter and abinary decoder connected to respective binary stages of said counter andhaving a plurality of outputs which are activated separately inaccordance with the binary count input.

3. An analog data recording apparatus as set forth in claim 2 furtherincluding means for providing a sync pulse just prior to the applicationof the first pulse of said repeating train of pulses and circuit meansresponsive to the application of said sync pulse for applying a resetpulse to a reset input of said counter.

4. An analog data recording apparatus as set forth in claim 3 whereinsaid switching means includes a plurality of flip-flops equal to saidplurality of outputs of said decoder, each of said flip-flops having atrigger input connected to the output of said comparator means and anenabling input connected to corresponding output of said decoder so thatwhen both said enabling input and said trigger input of one of saidflip-flops are activated simultaneously said flip-flop is set providinga signal at a set output thereof, a plurality of one-shot driversconnected to corresponding set outputs of said plurality of flip-flops,each of said drivers having an output connected to correspondinginputsof said markers of said recorder means.

5. An analog data recording apparatus as set forth in claim 4 whereinsaid variable reference voltage source decreases from a knownpositivevoltage and comparator means includes an amplifier for receivingnegative going data'pulses at an input thereof, a signal invertingcomparator, a first summing resistor connected between the output ofsaid amplifier and the input of said comparator, a second summingresistor connected between-said variable referencesource and the inputof said comparator, said comparator having an output connected to saidtrigger inputs of said plurality of flipflops, and a zener diodeconnected between the output of said comparator and ground so that theoutput of said comparatoris clamped'to ground as long as'said referencevoltage exceeds said negative going data pulses.

6. In combination with a high-speed photometric analyzer for measuringthe transmission of light through a plurality of discrete samplesdisposed in a spinning rotor and oriented in a circular array about thecenter of rotation of said rotor wherein a photodetector is positionedso as to sense the light transmitted through said samples as the samplesare rotated past the photodetector sensing position thereby generating arepeating train of data pulses whose amplitude is proportional to thelight transmitted through said samples, an analog data recordingapparatus for recording said train of data pulses in separate channelscomprising:

1 a comparator means for receiving said repeating train of pulses at aninput thereof and comparing the am- I plitude of each of said pulseswith a scanning reference voltage and providing a pulse at an outputthereofeach time the amplitude of one of said data signals exceeds saidreference voltage;

a mechanically driven variable voltage source having an output connectedto said comparator means for providing said scanning reference voltage;

means for generating reference pulses andrepeatedly, sequentially applyeach reference pulse to a plurality of separate outputs corresponding tothe number of data signals of said repeating train of pulses; pluralityof gating means equal to said plurality of outputs of said referencepulse generating means, each of said gating means having a trigger inputcommonly connected to the output of said comparator means and anenabling input connected to respective outputs of said reference pulsegenerating means for providing an output pulse at an output thereof thefirst time a pulse is applied to said second input thereof from saidreference pulse generating means in coincident with a pulse from saidcomparator means; recorder means including a linearly movable carriagehaving a plurality of electrically operated markers, each of saidmarkers having an input connected to respective outputs of saidplurality of gating means; a record medium disposed under said carriage;and a drive means mechanically coupled to said carriage and saidvariable voltage source for synchronously moving said carriage over saidrecord medium and adjusting the voltage output of said .variable voltagesource in a'scanning mode, whereby each of said markers is activated tomark said record medium ata distance from a reference position on saidrecord medium when the corresponding data signal exceeds said referencevoltage level of said variable voltage source. 7. The combination ofclaim. 6 further including means for generating a sync pulse just priorto the passing of a first one of said samples past said sensing positionand wherein'said reference pulse generating means includes a binarycounter, a binary decoder connected to respective binary stages of saidcounter and having a plurality of outputs which are activated separatelyin accordance with the binary count registered in said counter and acircuit means responsive to the application of said sync pulse forapplying a reset pulse to a reset input of said counter. v

8. The combination of claim 7 wherein said switching means includes aplurality of flip-flops equal to said plurality of outputs of saiddecoder, each of said flipflops having a trigger input connected to theoutput of said comparator means and an enabling input connected tocorresponding output of said decoder so that when both said enablinginput and said trigger input of one of said flip-flops are activatedsimultaneously said flip-flop provides a signal at the output thereof,and a plurality of one-shot drivers connected to corresponding outputsof said plurality of flip-flops, each of said drivers having an outputconnected to correpsonding inputs of said markers of said recordermeans.

9. The combination of claim 8 wherein said variable reference voltagesource decreases from a known positive voltage and comparator meansincludes an amplifier for receiving negative going data pulses at aninput thereof, a signal inverting comparator, a first summing resistorconnected between the output of said amplifier and the input of saidcomparator, a second summing resistor connected between said variablereference source and the input of said comparator, said comparatorhaving an output connected to said trigger inputs of said plurality offlip-flops, and a zener diode connected between the output of saidcomparator and ground so that the output of said comparator is clampedto 10 logarithmically with absorbance of said samples are compared witha logarithmic reference voltage so as to provide a direct recording ofabsorbance values of said samples on said record medium.

* ii I8

1. An analog data recording apparatus for recording a plurality of datasignals which are in the form of a continuously repeating train ofelectrical pulses of varying amplitude, comprising: a comparatoR meansfor receiving said repeating train of pulses at an input thereof andcomparing the amplitude of each of said pulses with a scanning referencevoltage and providing a pulse at an output thereof each time theamplitude of one of said data signals exceeds said reference voltage; amechanically driven variable voltage source having an output connectedto said comparator means for providing said scanning reference voltage;means for generating reference pulses and repeatedly, sequentially applyeach reference pulse to a plurality of separate outputs corresponding tothe number of data signals of said repeating train of pulses; aplurality of gating means equal to said plurality of outputs of saidreference pulse generating means, each of said gating means having atrigger input commonly connected to the output of said comparator meansand an enabling input connected to respective outputs of said referencepulse generating means for providing an output pulse at an outputthereof the first time a pulse is applied to said input thereof fromsaid reference pulse generating means in coincident with a pulse fromsaid comparator means; recorder means including a linearly movablecarriage having a plurality of electrically operated markers, each ofsaid markers having an input connected to respective outputs of saidplurality of gating means; a record medium disposed under said carriage;and a drive means mechanically coupled to said carriage and saidvariable voltage source for synchronously moving said carriage over saidrecord medium and adjusting the voltage output of said variable voltagesource in a scanning mode, whereby each of said markers is activated tomark said record medium at a distance from a reference position on saidrecord medium when the corresponding data signal exceeds said referencevoltage level of said variable voltage source.
 2. An analog datarecording apparatus as set forth in claim 1 wherein said reference pulsegenerating means includes a binary counter and a binary decoderconnected to respective binary stages of said counter and having aplurality of outputs which are activated separately in accordance withthe binary count input.
 3. An analog data recording apparatus as setforth in claim 2 further including means for providing a sync pulse justprior to the application of the first pulse of said repeating train ofpulses and circuit means responsive to the application of said syncpulse for applying a reset pulse to a reset input of said counter.
 4. Ananalog data recording apparatus as set forth in claim 3 wherein saidswitching means includes a plurality of flip-flops equal to saidplurality of outputs of said decoder, each of said flip-flops having atrigger input connected to the output of said comparator means and anenabling input connected to corresponding output of said decoder so thatwhen both said enabling input and said trigger input of one of saidflip-flops are activated simultaneously said flip-flop is set providinga signal at a set output thereof, a plurality of one-shot driversconnected to corresponding set outputs of said plurality of flip-flops,each of said drivers having an output connected to corresponding inputsof said markers of said recorder means.
 5. An analog data recordingapparatus as set forth in claim 4 wherein said variable referencevoltage source decreases from a known positive voltage and comparatormeans includes an amplifier for receiving negative going data pulses atan input thereof, a signal inverting comparator, a first summingresistor connected between the output of said amplifier and the input ofsaid comparator, a second summing resistor connected between saidvariable reference source and the input of said comparator, saidcomparator having an output connected to said trigger inputs of saidplurality of flip-flops, and a zener diode connected between the outputof said comparator and ground so that the output of said comparator isclamped to ground as long as saId reference voltage exceeds saidnegative going data pulses.
 6. In combination with a high-speedphotometric analyzer for measuring the transmission of light through aplurality of discrete samples disposed in a spinning rotor and orientedin a circular array about the center of rotation of said rotor wherein aphotodetector is positioned so as to sense the light transmitted throughsaid samples as the samples are rotated past the photodetector sensingposition thereby generating a repeating train of data pulses whoseamplitude is proportional to the light transmitted through said samples,an analog data recording apparatus for recording said train of datapulses in separate channels comprising: a comparator means for receivingsaid repeating train of pulses at an input thereof and comparing theamplitude of each of said pulses with a scanning reference voltage andproviding a pulse at an output thereof each time the amplitude of one ofsaid data signals exceeds said reference voltage; a mechanically drivenvariable voltage source having an output connected to said comparatormeans for providing said scanning reference voltage; means forgenerating reference pulses and repeatedly, sequentially apply eachreference pulse to a plurality of separate outputs corresponding to thenumber of data signals of said repeating train of pulses; a plurality ofgating means equal to said plurality of outputs of said reference pulsegenerating means, each of said gating means having a trigger inputcommonly connected to the output of said comparator means and anenabling input connected to respective outputs of said reference pulsegenerating means for providing an output pulse at an output thereof thefirst time a pulse is applied to said second input thereof from saidreference pulse generating means in coincident with a pulse from saidcomparator means; recorder means including a linearly movable carriagehaving a plurality of electrically operated markers, each of saidmarkers having an input connected to respective outputs of saidplurality of gating means; a record medium disposed under said carriage;and a drive means mechanically coupled to said carriage and saidvariable voltage source for synchronously moving said carriage over saidrecord medium and adjusting the voltage output of said variable voltagesource in a scanning mode, whereby each of said markers is activated tomark said record medium at a distance from a reference position on saidrecord medium when the corresponding data signal exceeds said referencevoltage level of said variable voltage source.
 7. The combination ofclaim 6 further including means for generating a sync pulse just priorto the passing of a first one of said samples past said sensing positionand wherein said reference pulse generating means includes a binarycounter, a binary decoder connected to respective binary stages of saidcounter and having a plurality of outputs which are activated separatelyin accordance with the binary count registered in said counter and acircuit means responsive to the application of said sync pulse forapplying a reset pulse to a reset input of said counter.
 8. Thecombination of claim 7 wherein said switching means includes a pluralityof flip-flops equal to said plurality of outputs of said decoder, eachof said flip-flops having a trigger input connected to the output ofsaid comparator means and an enabling input connected to correspondingoutput of said decoder so that when both said enabling input and saidtrigger input of one of said flip-flops are activated simultaneouslysaid flip-flop provides a signal at the output thereof, and a pluralityof one-shot drivers connected to corresponding outputs of said pluralityof flip-flops, each of said drivers having an output connected tocorrepsonding inputs of said markers of said recorder means.
 9. Thecombination of claim 8 wherein said variable reference voltage sourcedecreases from a known positive voltage and comparatoR means includes anamplifier for receiving negative going data pulses at an input thereof,a signal inverting comparator, a first summing resistor connectedbetween the output of said amplifier and the input of said comparator, asecond summing resistor connected between said variable reference sourceand the input of said comparator, said comparator having an outputconnected to said trigger inputs of said plurality of flip-flops, and azener diode connected between the output of said comparator and groundso that the output of said comparator is clamped to ground as long assaid reference voltage exceeds said negative going data pulses.
 10. Thecombination of claim 9 wherein said variable reference voltage sourcevaries logarithmically with respect to the linear movement of saidcarriage so that the transmittance signals of said samples which varylogarithmically with absorbance of said samples are compared with alogarithmic reference voltage so as to provide a direct recording ofabsorbance values of said samples on said record medium.